1. Field of the Invention(s)
The present invention(s) relate to synchronization, and more particularly, to systems and methods for network synchronization.
2. Description of Related Art
Synchronized time information is important for distributed systems, particularly those containing distributed components networked together using wired or wireless networks (e.g., a microwave network). Synchronous Ethernet (SyncE) is just one solution utilized in distributing clock synchronization information over a network. SyncE is an ITU-T standard for transporting a clock signal over an Ethernet network layer. ITU-T G.8261 defines the architecture of SyncE networks, and ITU-T G.8262 specifies Synchronous Ethernet clocks for SyncE (i.e., specifies G.8262-compliant clock signal). According to its specification, SyncE is designed to be compatible with Synchronous Digital Hierarchy (SDH) networks.
The Precision Time Protocol (PTP), as described in IEEE 1588, is another method for synchronizing clocks of distributed components over a network. Under PTP, clock distribution is facilitated through a master-slave architecture using one or more clocks. According to PTP, an ordinary clock is a network device that has a single network connection and that is either a source (mater node) or a destination (slave node) for clock synchronization reference over PTP. A boundary clock is a network device that has multiple network connections and that is used to bridge clock synchronization between different network segments using PTP. A transparent clock is a device that modifies PTP messages (e.g., modifies message timestamp) as they pass through the device. When a network consists of IEEE 1588 aware devices (i.e., ordinary clocks, boundary clocks, or transparent clocks), high precision clock synchronization can be obtained with very simple clock servo algorithms to determine rate adjustments and time corrections. With PTP, sophisticated processing is not necessary as only simple averaging or filtering of the protocol measurements is required.
Though use of PTP has very low demands on local clocks and networks, in order to implement PTP, the components on the network must be configured (i.e., include additional hardware and/or firmware) to take advantage of PTP. When a network consists of devices that are not IEEE 1588 aware, packet delay variation (PDV) is often present and can be significant. Additionally, clock synchronization using PTP requires feedback from a slave node to a master node and, at times, may require recovery at the slave node of both the frequency and the phase of the clock at a master node in order to synchronize a clock at the slave node.